Nowadays mobile telephone systems are known among them the well-known GSM system. The mobile phones used in this system comprise a SIM card (Subscriber Identity Module) for controlling them, the SIM card containing relevant information, such as subscriber details, security information, memory for a personal directory of numbers, and data that identify the user to the network provider and allows the access to the wireless communication network, such as a GSM or a G3 network. A SIM card has associated the IMSI and the MSISDN, IMSI (International Mobile Subscriber Identity) being a unique number for identifying a subscriber in the network and MSISDN (Mobile Station ISDN number) being the phone number.
Dual SIM cards are known in the GSM system. Dual SIM cards are a utility that allows GSM users to have two SIM cards with the same number, i.e. with the same IMSI and MSISDN. The dual SIM can be used independently on two mobile phones. The idea is that either one of the phones is in use.
Mobile phones regularly contact the network for a location update, so that the network is informed in which cell of the cellular network the phone is presently located and can be contacted.
The use of the dual SIM cards has a drawback in that, when inadvertedly both mobile phones are in use, the last location updated mobile phone is the only one receiving the next call, so there is an undefined situation. If a user has left an active phone e.g. back at home, and is away from home with the second active phone, a call would be received on the phone with the most recent location update. This could well be the unattended phone back home, and the user could at least temporarily not be reached by phone.
EP 1 170 969 discloses a method and apparatus for remotely switching into a secure mode a mobile electronics device when it has been lost, stolen or misused in order to prevent its use except to help the owner find it. This can be achieved using a control message, for example, via a Short Messaging System (SMS).
This method allows to remotely lock a mobile phone for user access when it has been lost but doesn't solve the drawback of the dual SIM cards because the mobile phone needs to be active and subscribed to the network to help the user to find it.
U.S. Pat. No. 5,987,609 discloses a system for remotely securing or locking a stolen wireless information device via an email message with an attached password to the device. The owner of an information device specifies a password beforehand, which is stored in a memory. When an electronic mail is received from another information device through a wireless telephone facility of the information device, a password attached to the email message is checked with the password stored in the memory. When the password match occurs, a security process is executed.